Cell Phone law suit

* ACLU questions tracking suspects by cellphone location

* Case is latest in privacy versus technology disputes

* Appeals court upholds ruling against Justice Department

By Jeremy Pelofsky and James Vicini

WASHINGTON, Sept 6 (Reuters) - The U.S. government must tell the public how it tracked suspects by cellphone without having given a judge detailed reasons for the tracking in some cases, an appeals court ruled on Tuesday, in a case pitting new technology against privacy rights.

A leading civil liberties group claimed victory in one of several cases making its way through the court system weighing privacy rights against law enforcement using data available through the proliferation of new technologies like the Global Positioning System (GPS), cellphones and laptop computers.

"I highly doubt that the 90 percent of Americans who carry cell phones thought that when they got cellphone service they were giving up their privacy in their movements," said Catherine Crump, a lawyer for the American Civil Liberties Union who argued the case.

The group has argued that prosecutors are getting information about a suspect's location with a judge's approval -- but without a warrant providing probable cause, which is typically needed in criminal cases for a warrant.

The ACLU questioned how often prosecutors have used applications for such information and sued to get details, a challenge the Justice Department said would violate the privacy of those under investigation or prosecuted.

A federal judge in 2010 ruled the Justice Department must reveal those cases that used such information in which the suspect was convicted, a decision upheld by a three-judge panel of the U.S. Court of Appeals for the District of Columbia.

"The disclosure sought by the plaintiffs would inform this ongoing public policy discussion by shedding light on the scope and effectiveness of cell phone tracking as a law enforcement tool," Judge Merrick Garland wrote in the unanimous decision.

APPEAL POSSIBLE

Disclosure would, for example, provide information about the kinds of crimes the government uses cellphone tracking data to investigate, the appeals court said.

Citing privacy rights, the district court judge refused to order the government to reveal other cases in which such applications were used, such as the acquittal of a suspect or a sealed case.

The appeals court sent that issue back to the lower court for more proceedings to determine the extent of those cases.

The Justice Department could appeal the ruling to the full appeals court or to the Supreme Court, which already has agreed to consider another privacy case involving new technology.

Later this year the Supreme Court will hear arguments over whether law enforcement should have obtained a warrant before attaching a GPS device to a suspect's vehicle.

Justice Department spokesman Charles Miller said the agency was reviewing the decision and had not decided on its next step.

After surveying several U.S. Attorneys' offices, the Drug Enforcement Agency and the Justice Department, some 255 cases were identified in which an application for cellphone location information was used.

The government has offered to identify the nature of the charges as well as whether a motion to suppress that information was filed and the outcome. The ACLU said it was open to ideas on how to provide the public details of the information as a possible settlement. (Editing by Howard Goller and Eric Walsh)